DNA replication

DNA replication is a semilconservative replication where a double helix replicates 2 daughter strands where each of the daughter strands has one old strand and one newly made strand.

Steps of DNA replication

1. DNA helicase unwinds and unzips the double helix by breaking hydrogen bonds.

2. At the same time, DNA gyrase relieves the tension in the DNA

3. After the DNA is separated into  2 single stranded DNA, which is very unstable. Therefore, single-stranded binding proteins(SSB) prevents DNA from degenerate.

4.RNA primase attaches itself to DNA after its unzipped and creates primer.

5. Primer acts as a signal to sign DNA polymerase 3 to attach nucleoside to the 3' end of unzipped single DNA strand.

6. There are 2 different types of replication going at this stage.
At the lagging strand, which grows away from the replication fork, there are many  okazaki fragments formed in order to let the DNA strand to grow in 5' to 3' direction. At the leading strand, which grows towards the replication fork, the newly formed DNA strand grows continuously in 5' to 3' direction.

7. Once the polymerase 3 finishes to replicate, polymerase 1 comes in to remove the primase and attach correct nucleosides at the gap. In addition, it checks the mistakes in the replicated strands.

8. Lastly, DNA ligase glues the gap between okazaki fragments in the lagging strand with the phosphodiester bond.


NOTE: LIST OF ENZYMES USED IN DNA REPLICATION
Helicase
Gyrase
Primase
DNA polymerase 3
DNA polymerase 1
Ligase

VIDEO CLIP OF REPLICATION
http://www.youtube.com/watch?v=teV62zrm2P0